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I am looking to use a piece of PVC as the center insulator of a vertical
dipole I'm planning to put up. Anyone know the insulating
characteristics of this stuff? It's not going to conduct significantly
@ hf when wet?? Thanks for the help.

gary

"Angela & Gary" wrote in message
...
I am looking to use a piece of PVC as the center insulator of a vertical
dipole I'm planning to put up. Anyone know the insulating
characteristics of this stuff? It's not going to conduct significantly
@ hf when wet?? Thanks for the help.

gary

It works fine.
I used a short piece of pvc to connect 2 pieces of aluminum conduit.
I fed the coax thru one end of the alum conduit to have a vertical dipole
fed from inside where the 3 pieces come together

On Sat, 19 Feb 2005 13:14:55 -0800, Angela & Gary
wrote:

I am looking to use a piece of PVC as the center insulator of a vertical
dipole I'm planning to put up. Anyone know the insulating
characteristics of this stuff? It's not going to conduct significantly
@ hf when wet?? Thanks for the help.

gary


It will work great. If you want to test it, microwave a piece of the
material for 1 minute. IF it gets very warm, you may want a different
material. The white pvc should work as well as you need and then
some.


--
73 for now
Buck
N4PGW

I'd also add a glass of water in the microwave when you do
that...I'm not sure if they are still that way, but it used
to be bad for them to run with no load...IE: food...MK

It's not clear to me how you correlate how warm something gets in the
microwave oven with how much loss it'll incur at the end of an HF
antenna. Maybe someone can explain this.

Roy Lewallen, W7EL

wrote:
I'd also add a glass of water in the microwave when you do
that...I'm not sure if they are still that way, but it used
to be bad for them to run with no load...IE: food...MK

On Mon, 21 Feb 2005 03:55:43 -0800, Roy Lewallen
wrote:

It's not clear to me how you correlate how warm something gets in the
microwave oven with how much loss it'll incur at the end of an HF
antenna. Maybe someone can explain this.

Roy Lewallen, W7EL

The microwave works with RF to heat the 'food'. If an object absorbs
RF, it does so as heat, therefore, if you subject it to intense RF by
using a microwave oven, it will heat up. If it heats up, it is
affecting the antenna's radiation.

Depending on how it is connected to the antenna and type of antenna,
it may not make a noticeable difference on the signal, but in many
cases, especially where the wire is running along with or inside of a
material such as PVC, the material may have a detrimental impact on
the signal or SWR.

Not being aware of this a long time ago, I built a two meter half-wave
vertical dipole by dropping a line of wire into a piece of CPVC and
capping it off. My mobile 5/8 wave whip on the car, twelve feet below
it, using the same rig has much much better reception and signal than
the dipole. I plan to replace that antenna with a similar dipole using
1/2 inch copper tubing.

When I nuke the cpvc for one minute, it gets warm to the touch. I
don't expect to melt it using my 706, but I do have a couple of
repeaters I can't hear from that antenna that I would like to reach.

73 for now
Buck
N4PGW

--
73 for now
Buck
N4PGW

On Mon, 21 Feb 2005 03:55:43 -0800, Roy Lewallen
wrote:

It's not clear to me how you correlate how warm something gets in the
microwave oven with how much loss it'll incur at the end of an HF
antenna. Maybe someone can explain this.


Dear Roy,
Perhaps that is not the objective, Roy - maybe the rationale' is
simply to decide whether or not a particular sample of material is a
"high loss" dielectric or not.

Regards,

Bob, W9DMK, Dahlgren, VA
Replace "nobody" with my callsign for e-mail
http://www.qsl.net/w9dmk
http://zaffora/f2o.org/W9DMK/W9dmk.html

Bob, W9DMK wrote:
"-maybe the rationale is simply to decide whether or not a particular
sample of material is a "high loss" or not."

I think that`s it. The properties of dielectrics are functions of
temperature and frequency. My CRC Handbook of Chemistry and Physics
shows PVC`s dielectric constant is definitely a function of frequency,
unlike polystyrene and some other pastics.

I`ve seen PVC used as a base insulator for vertical elements of a HF
antenna array, and it worked OK.

I think low power factor and dissipation=A0are desirable for an
insulator. My 1987 edition of the ARRL Handbook has a table 47 on pages
35-36 and 35-37 titled "Properties of Common Thermoplastics. Maybe later
editions have expanded tables.

Best regards, Richard Harrison, KB5WZI

Buck wrote:
On Mon, 21 Feb 2005 03:55:43 -0800, Roy Lewallen
wrote:


It's not clear to me how you correlate how warm something gets in the
microwave oven with how much loss it'll incur at the end of an HF
antenna. Maybe someone can explain this.

Roy Lewallen, W7EL


The microwave works with RF to heat the 'food'. If an object absorbs
RF, it does so as heat, therefore, if you subject it to intense RF by
using a microwave oven, it will heat up. If it heats up, it is
affecting the antenna's radiation.

No, that's not correct. If you heat up an object in the microwave oven,
it indicates that an object of that material, size, and shape absorbs
some fraction (how large a fraction, you have no idea) of energy when an
intense microwave field is applied. It says nothing about what that
object will do when put at the end of an HF antenna, where it isn't
exposed to an intense microwave field.

Depending on how it is connected to the antenna and type of antenna,
it may not make a noticeable difference on the signal, but in many
cases, especially where the wire is running along with or inside of a
material such as PVC, the material may have a detrimental impact on
the signal or SWR.

Why yes, it might, or it might not. This can be said of any material.

Not being aware of this a long time ago, I built a two meter half-wave
vertical dipole by dropping a line of wire into a piece of CPVC and
capping it off. My mobile 5/8 wave whip on the car, twelve feet below
it, using the same rig has much much better reception and signal than
the dipole. I plan to replace that antenna with a similar dipole using
1/2 inch copper tubing.

When I nuke the cpvc for one minute, it gets warm to the touch. I
don't expect to melt it using my 706, but I do have a couple of
repeaters I can't hear from that antenna that I would like to reach.

That's an interesting anecdode, but it hardly supports the contention
that there's a direct correlation between heating in a microwave oven
and detraction of performance of an HF antenna when used as an end
insulator.

Roy Lewallen, W7EL

W9DMK (Robert Lay) wrote:
On Mon, 21 Feb 2005 03:55:43 -0800, Roy Lewallen
wrote:


It's not clear to me how you correlate how warm something gets in the
microwave oven with how much loss it'll incur at the end of an HF
antenna. Maybe someone can explain this.



Dear Roy,
Perhaps that is not the objective, Roy - maybe the rationale' is
simply to decide whether or not a particular sample of material is a
"high loss" dielectric or not.

Is a material that is "high loss" at microwave frequencies always "high
loss" at HF? How "high" does the loss have to be in order to detract
from an HF antenna's performance when used as an end insulator? When you
put an object in the microwave oven for a minute with a glass of water
and the temperature rises 10 degrees C, how "high" is the loss? How
"high" is the loss at HF?

Roy Lewallen, W7EL

On Mon, 21 Feb 2005 10:33:29 -0800, Roy Lewallen
wrote:
Is a material that is "high loss" at microwave frequencies always "high
loss" at HF? How "high" does the loss have to be in order to detract
from an HF antenna's performance when used as an end insulator? When you
put an object in the microwave oven for a minute with a glass of water
and the temperature rises 10 degrees C, how "high" is the loss? How
"high" is the loss at HF?

You're right, it doesn't even qualify as a SWAG! Hi!

Bob, W9DMK, Dahlgren, VA
Replace "nobody" with my callsign for e-mail
http://www.qsl.net/w9dmk
http://zaffora/f2o.org/W9DMK/W9dmk.html

It probably doesn't. I had just heard it was a way
to tell if the PVC had some kind of metal particals,
or whatever. I'm not that much up on PVC, but the rumor
I had heard was the "grey" PVC was better for HF rf use
compared to the white stuff. But I don't really know.
I've tried both, and never had any problems. The loading
coil on my shorter mobile antenna is wound on grey PVC,
and so far, I've never noticed any adverse effects.
My 2nd antenna uses a thin plastic tube, about like what
you would see on a sidewalk blower, or whatever...
Never noticed any problems with it either. I seem to have
about the same performance as an open frame coil, as far
as I can tell, and I've never noticed any heating, or
melting, etc..
My comment was more to protect the microwave, rather
than endorse the value of PVC nuking...:/ I have
tried it though...The grey stuff does stay cold when
nuked...Whatever thats worth..I didn't try the white
though...I've never had trouble with any material as far
as end insulators...I've run legal limit through plastic
coathangar insulators 3 inches long, and didn't arc...
That I could tell anyway...Same for PVC or wood...
The only time I've ever arced, was when the bare wire was
actually rubbing a tree branch...I started to burn it
up...Probably had been that way 2 weeks before I noticed
it..
MK

Roy Lewallen wrote:
Is a material that is "high loss" at microwave frequencies
always "high loss" at HF?

Roy, we know you are into quantitative stuff but some
of us are into qualitative stuff. We know not to put
our hands into a flame even though we have no idea what
is the temperature of the flame or what temperature our
hands reach when put into a flame. If the exact temperature
of a flame Vs a blister on your skin is important to you,
why not experiment and report? :-)
--
73, Cecil http://www.qsl.net/w5dxp

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On Mon, 21 Feb 2005 03:55:43 -0800, Roy Lewallen
wrote:

It's not clear to me how you correlate how warm something gets in the
microwave oven with how much loss it'll incur at the end of an HF
antenna. Maybe someone can explain this.

Roy Lewallen, W7EL

The microwave test was written up in Hints & Kinks, 13th edition, page
6-6, although no scientific explanation was given as to why warmed
plastic would be worse than cool, after 2-3 minutes nuking on "high"
with a cup of water also present. (Author was E.R. Berg, KZ9Y.)

bob
k5qwg



wrote:
I'd also add a glass of water in the microwave when you do
that...I'm not sure if they are still that way, but it used
to be bad for them to run with no load...IE: food...MK